Hydraulic Cover Stones

(HCS)

THIS METHOD IS A DAVE DERRICK

DISCOVERY (DDD)

Hydraulic Cover Stones (HCS) are typically large single stones placed in a flowing channel with the crest of the stone within inches of the base flow water surface elevation.

The constant movement & rippling of the water from the Hydraulic Cover Stones results in a type of cover, “hydraulic cover”, masking fish location from the view of predators. The stones also provide resting areas & within-channel refugia for fish during high energy, high-flow events.

Hydraulic Cover Stones are especially useful in sections of the stream with little in-channel structure, or vegetative cover, or undercut banks.

Hydraulic Cover Stones (HCS)

Large single stones placed in a flowing channel. Three versions:

1.) Top of the stone set at an elevation slightly lower than the typical base-flow water surface elevation. When sited correctly, the accelerated flow over the top of the stone will change from subcritical to supercritical flow, & immediately downstream back to subcritical (usually with a weak hydraulic jump). The hydraulic jump will entrain air & help aerate the stream.

2.) Stone crest set just below the base flow water surface elevation results in an acceleration of the water moving over the top of the stone, with “standing waves” (stationary waves) forming downstream of the stone.

3.) Stone crest set slightly above the base flow water surface, resulting in a V-shaped wake and flow split with a double return eddy flow pattern DS of the stone. However, these emergent stones might be used as perches for predators.

Hydraulic Cover Stones (HCS)

Hydraulic Cover Stones provide improved aquatic habitatHydraulic Cover Stones provide improved aquatic habitat

Hydraulic Cover Stones shown functioning 3 different ways. Graphics courtesy of Ecology & Environment, Inc.

UNKNOWN AGE – CEDAR RIVER, SEATTLE, WA-DERRICK 8-22-2012

UNKNOWN AGE – Looking US @ a boulder acting as a HCS. Split flow, acceleration, air entrainment, & dead water DS of boulder.

Functions of Hydraulic Cover Stones• Provides micro-topography (scour & deposition)• Provides diversity of velocities• Provides “hydraulic cover” turbulence, surface water

disturbance (boat wake), return currents, eddy fences, internal distortion, pressure zones, undulating surface water, standing waves, etc.

• Provides feeding lanes for fish• Provides shape cover & solid substrate for benthics• Provides refugia during high flow events• Dissipates energy • Can aerate water, or de-gas super-saturated water

Boulder Clusters typically consist of a number of very large stones closely arranged in some type of pattern. The Boulder Cluster usually blocks a fair amount of the stream, with stone

crest heights 2 to 3 ft above the base flow water surface elevation. Hydraulic Cover

Stones are single large stones with the crest heights within inches of the base flow water surface elevation. HCS block a very small

percentage of the cross-section of the stream.

Shadow depositional

sand bar splits flow, resulting in both banks eroding in a

straight stretch. Little Sugar Creek

one year after placement

(1998).

This was not the designer’s

intent.

Some concerns with Boulder Clusters (cluster too wide & tall here in a high bed-load stream)

(Purloined from Andrew Burg)

Possible Problems with Boulder Cluster designs:

1. Excessive scour buries boulder

2. Cluster blocks large percentage of stream flow

3. Cluster redirects stream energy in unwanted direction (s)

4. Excessive deposition DS of cluster

5. Cluster too high, provides perches for predators/fishermen

(www.E-senss.com)

Natural Hydraulic Cover Stones (HCS) on the Genesee River, Letchworth Park, NY

photo taken 2003. Hydraulic Cover Stone at Elton Creek, NY

Flow

Flow

Hydraulic Cover Stones on Eighteenmile Creek Project, Newfane, NY

(constructed Sept. 2003)

Close-up of large stones to be used as HCS, these were hand selected, minimum 3 ft by 3 ft.

My sneaker

A Hydraulic Cover Stone (HCS) dug into the stream bed substrate for stability. The

downstream wake is the “Hydraulic Cover”.

Flow

HCS

In a sand-silt bed stream, deeper excavation, or reinforcement of the substrate, might have to be accomplished so that bed

scour does not cause the HCS to sink into the substrate.

Flow

HCS

Here comes Jimmy with a Hydraulic Cover Stone (HCS)!! Water depths were measured & the correct thickness of stone selected for this specific location

Water depth was measured, & a specific

sized rock delivered

Carefully placing the Hydraulic Cover Stone

Bed was dug & stone placed in hole.

Sediment near stone acting as a dye trace.

Flow

Flow

First HCS placed in Eighteenmile Cr., turbulence,

energy dissipation, eddy fences…

Looking DS, note locations of Hydraulic Cover Stones during unusually low flow

conditions

Crazy turbulence surrounds a HCS

Trio of Hydraulic Cover Stones working beautifully, note those wakes (the hydraulic cover)

This is a cobble-bed stream. This technique might not

work as well in a sand-bed stream (stones could subside)

Locals say this is the best fishing area in

the creek (US of Cover Stones)

HCS using up stream energy & entraining air into flowing water

Flow from left to right, note the hydraulic jump @ the Hydraulic Cover Stone

Same Hydraulic Cover Stone, close up

Looking US at a Hydraulic

Cover Stone

Multi-Use Hydraulic Cover

Stones, in this case a fisherman’s

resting rock, (FRR)

Salmon fishermen concentrating efforts among the Hydraulic Cover Stones,

Eighteenmile Creek, Newfane, NY, Oct 2003

Fish those Hydraulic Cover Stones !!!!!!!!

NO NEED FOR A NET (if you’re good)(FISH ON !!!)

On Saturday 10-19-03 (during the salmon run) folks are everywhere, 353 recreators by 9:30am.

Hydraulic Cover Stones on Cattaraugus Creek

@ Savage Road, Sardinia, New York

Hydraulic Cover Stones for stable pre-dug “Pocket” scour holes in shallow areas

(riffles & shallow runs)

• Increases depths• Provides microtopography• Provides diversity of velocities• Provides hydraulic cover• Provides shape cover• Provides in-channel refugia• Dissipates stream energy

Catt Creek, looking US at riffle-run, measuring how high the Hydraulic Cover Stone will jut into current.

Hydraulic Cover Stone in pre-dug scour hole, stones measured to fit

Looking US at a series of Hydraulic Cover Stones, took 50 minutes to install 9 stones

Looking DS at same Hydraulic Cover Stones located in “run” section of stream. Previous condition was shallow sheet-type flow

A close look at a hard working Hydraulic Cover Stone during a high water event, Cattaraugus Cr. at Savage Rd. 11/4/2004

Mini-Case Study: 1 of 3

Stone is here

But relatively calm right at the Hydraulic Cover

Stone, energy dissipated!!

Downstream of HCS fierce currents (water piling up on

hip boots & bent pole)

Mini-Case Study: 2 of 3

Same Hydraulic Cover Stone during base flow conditions, not

very impressive considering observed function during high flow

Mini-Case Study: 3 of 3

On 11-11-2010 a series of short test runs were performed on a small 4 inch wide sand-bed hydraulic flume @ the State University of New York at Buffalo (UB). Flow duration ranged from 20 minutes to 45

minutes or so. Flow stage was supposed to mimic the Q-2 flow, but varied when we forgot to turn on the

inflow hose & add water as the flume leaked. Our feet got wet. Discharge was varied a bit & not written

down. Otherwise very scientific!!

Hydraulic Cover Stone Quick & Dirty Flume Tests @ UB

Looking US @ the flume & flume-meister, Dr. Sean Bennett

SEAN BENNETT’S FLUME @ UB – ENTIRE FLUME - PIX DAVE DERRICK 11-11-2010

THE EFFECTS OF STONE SIZE &

ROUGHNESS ON NEAR-FIELD SCOUR AROUND A SINGLE HYDRAULIC

COVER STONE

Looking @ 3 Hydraulic Cover Stones. The upstream stone is small & aerodynamic resulting in very little scour. More scour as each downstream HCS is progressively larger & blocks more flow

SEAN BENNETT’S FLUME @ UB – HYDRAULIC COVER STONES-DERRICK 11-11-10

Looking @ a single HCS. The US face of the stone is square & vertical. Scour was so great US of the stone that it fell US into its scour hole!!! LESSON: SIZE & SHAPE MATTER GREATLY!

SEAN BENNETT’S FLUME @ UB – HYDRAULIC COVER STONES-DERRICK 11-11-10

This PowerPoint presentation was developed & built by Dave Derrick.

Any questions or comments, call my personal cell @ 601-218-7717, or email @ d_derrick@r2d-eng.com

Enjoy the information!!

Speaking of size, presented

here is Jackson Danger Rainer

wearing Uncle Brent’s huge

size 14 sneakers